U.S. patent application number 11/536292 was filed with the patent office on 2008-04-03 for methods to accelerate photoimageable material stripping from a substrate.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Han-Wen Chen, Roman Gouk, James S. Papanu, Phillip Peters.
Application Number | 20080078424 11/536292 |
Document ID | / |
Family ID | 39259933 |
Filed Date | 2008-04-03 |
United States Patent
Application |
20080078424 |
Kind Code |
A1 |
Gouk; Roman ; et
al. |
April 3, 2008 |
METHODS TO ACCELERATE PHOTOIMAGEABLE MATERIAL STRIPPING FROM A
SUBSTRATE
Abstract
Embodiments of methods for decreasing the process time for
photoresist stripping from photomasks are herein disclosed. In some
embodiments, a stripping solution and a cleaning solution are
consecutively applied in an alternating manner to a photomask to
remove photoresist from the mask. The stripping solution and the
cleaning solution can each be applied between 6 and 12 times. The
stripping solution and the cleaning solution can be applied in a
predetermined time interval from about 30 seconds to about 120
seconds and from about 8 seconds to about 30 seconds, respectively.
The process can include a finishing process which can include a
final cleaning operation, a rinsing operation and a drying
operation.
Inventors: |
Gouk; Roman; (San Jose,
CA) ; Peters; Phillip; (Santa Clara, CA) ;
Chen; Han-Wen; (San Mateo, CA) ; Papanu; James
S.; (San Rafael, CA) |
Correspondence
Address: |
APPLIED MATERIALS/BLAKELY
1279 OAKMEAD PARKWAY
SUNNYVALE
CA
94085-4040
US
|
Assignee: |
APPLIED MATERIALS, INC.
|
Family ID: |
39259933 |
Appl. No.: |
11/536292 |
Filed: |
September 28, 2006 |
Current U.S.
Class: |
134/26 ;
134/29 |
Current CPC
Class: |
G03F 7/423 20130101;
H01L 21/67057 20130101; H01L 21/6708 20130101; H01L 21/67028
20130101; H01L 21/67051 20130101 |
Class at
Publication: |
134/26 ;
134/29 |
International
Class: |
B08B 3/00 20060101
B08B003/00 |
Claims
1. A method comprising: providing a substrate comprising a
photoimageable material thereon; applying a first stripping
solution to the photoimageable material; after applying the first
stripping solution, applying a first cleaning solution to the
photoimageable material; after applying the first cleaning
solution, applying a second stripping solution to the
photoimageable material; after applying the second stripping
solution, applying a second cleaning solution to the photoimageable
material; and rinsing the substrate.
2. The method of claim 1, further comprising, prior to the rinsing,
performing a final cleaning operation to the substrate.
3. The method of claim 1, further comprising, after the rinsing,
performing a drying operation to the substrate.
4. The method of claim 1, wherein the cleaning solution comprises
an ammonium peroxide mixture solution.
5. The method of claim 4, wherein the ammonium peroxide mixture
solution is one of Standard Clean 1 or AM-clean.
6. The method of claim 1, wherein at least one of the first and
second stripping solutions is an ozone deionized water solution
between 15 parts per million and 80 parts per million.
7. The method of claim 1, further comprising alternately applying
at least one of the first or second stripping solutions and at
least one of the first or second cleaning solutions between 6 and
12 times each.
8. The method of claim 1, wherein at least one of the first or
second stripping solutions and at least one of the first or second
cleaning solutions is applied in a predetermined time interval.
9. The method of claim 8, wherein at least one of the first or
second stripping solutions is applied between 30 seconds and 120
seconds and at least one of the cleaning solutions is applied
between 8 seconds and 30 seconds.
10. The method of claim 9, wherein at least one of the first or
second stripping solutions is applied between 45 seconds and 65
seconds and at least one of the cleaning solutions is applied for
10 seconds.
11. The method of claim 1, wherein the photoimageable material is
one of a positive photoresist and a negative photoresist.
12. The method of claim 1, wherein the photoimageable material is
patterned on the substrate.
13. The method of claim 1, wherein the photoimageable material is
between 3000 Angstroms and 50,000 Angstroms.
14. The method of claim 1, wherein the substrate is a glass plate
coated on one side with a chrome-containing material or a quartz
plate coated on one side with a chrome-containing material.
15. The method of claim 1, wherein a total processing time is
between 6 minutes and 15 minutes.
16. The method of claim 1, wherein the final cleaning operation is
performed with AM-clean, the rinsing operation is performed with
deionized water, and the drying operation is spin drying.
17. The method of claim 1, wherein the first stripping solution and
the second stripping solution are the same.
18. A method comprising: applying a stripping solution comprising
ozone deionized water at 20 parts per million to a substrate with a
photoimageable material thereon during a first time interval;
applying a cleaning solution comprising an ammonium hydroxide
solution to the substrate during a second time interval; and
repeating the applications in consecutive intervals prior to
performing a final cleaning operation, a rinsing operation and a
drying operation to the substrate.
19. The method of claim 18, wherein the ammonium hydroxide solution
is AM-clean comprising a solution of AM1/hydrogen
peroxide/deionized water at a ratio of 1:2:80 wherein the AM-1 is
28% to 29% by weight of ammonia to water and the hydrogen peroxide
is from about 31% to 32% by weight of hydrogen peroxide to
water.
20. The method of claim 18, wherein the repeating is between 6 and
12 times.
21. The method of claim 18, wherein the total application time is
less than 15 minutes.
22. The method of claim 18, wherein the first time interval is
between 30 seconds and 120 seconds.
23. The method of claim 18, wherein the second interval is between
8 seconds and 15 seconds.
24. The method of claim 18, wherein the photoimageable material is
one of a positive photoresist and a negative photoresist.
25. The method of claim 18, wherein the photoimageable material is
patterned on the substrate.
26. The method of claim 18, wherein the photoimageable material is
between 3000 Angstroms and 50,000 Angstroms.
27. The method of claim 18, wherein the substrate is a glass plate
coated on one side with a chrome-containing material or a quartz
plate coated on one side with a chrome-containing material.
28. The method of claim 18, wherein the final cleaning operation is
performed with AM-clean, the rinsing operation is performed with
deionized water, and the drying operation is spin drying.
Description
FIELD OF INVENTION
[0001] Photomask processing.
BACKGROUND OF INVENTION
[0002] A "photoresist" is a light-sensitive organic polymer that is
exposed by the photolithography process, then developed to produce
a pattern which identifies some areas of the film to be etched.
Photoresists are typically either negative or positive. Photoresist
compositions are used in microlithographic processes for making
miniaturized electronic components, such as in the fabrication of
semiconductor device structures. The miniaturized electronic device
structure patterns are typically created by transferring a pattern
from a patterned masking layer overlying the semiconductor
substrate rather than by direct write on the semiconductor
substrate because of the time economy which can be achieved by
blanket processing through a patterned masking layer. With regard
to semiconductor device processing, the patterned masking layer may
be a patterned photoresist layer or may be a patterned "hard"
masking layer (typically an inorganic material or a high
temperature organic material) which resides on the surface of the
semiconductor device structure to be patterned. The patterned
masking layer is typically created using another mask which is
frequently referred to as a photomask. A photomask is typically a
thin layer of a metal-containing layer (such as a
chrome-containing, molybdenum-containing, or tungsten-containing
material, for example) deposited on a glass or quartz plate. The
photomask is patterned to contain a "hard copy" of the individual
device structure pattern to be recreated on the masking layer
overlying a semiconductor structure.
[0003] A photomask may be created by a number of different
techniques, depending on the method of writing the pattern on the
photomask. Due to the dimensional requirements of current
semiconductor structures, the writing method is generally with a
laser or e-beam. A typical process for forming a photomask may
include: providing a glass or quartz plate, depositing a
chrome-containing layer on the glass or quartz surface, depositing
an antireflective coating (ARC) over the chrome-containing layer,
applying a photoresist layer over the ARC layer, direct writing on
the photoresist layer to form a desired pattern, developing the
pattern in the photoresist layer, etching the pattern into the
chrome layer, and removing the residual photoresist layer. Advanced
photomask manufacturing materials frequently include combinations
of layers of materials such as chromium, chromium oxide, chromium
oxynitride, molybdenum, molybdenum silicide, and molybdenum
tungsten silicide.
[0004] Processes for removing photoresist from a photomask include
both dry stripping and wet stripping. Dry stripping can be
performed in a chamber with oxygen (O.sub.2) based plasmas at a
temperature below 150.degree. C. Stripping of positive photoresists
from a photomask has been shown to be relatively successful by
visual inspection. On the other hand, stripping of negative
photoresists requires an additional wet stripping process. For
either type of photoresist, it has been reported that plasma
stripping with an oxygen based chemistry can result in degradation
of the chromium oxide anti-reflective layer. Wet stripping can
typically be performed using a process of applying a stripping
solution and a subsequent cleaning solution to the photomask. This
method can be very time consuming since the stripping solution
removes the photoresist by oxidation and breaking carbon bonds, but
not actually dissolving the photoresist. The photoresist is removed
by being dissociated into lower molecular weight components (or
oxidized completely to C.sub.ox) and subsequently rinsed off with
the cleaning solution. The process can take up to 40 minutes and
decreases the production rate of photomasks.
[0005] In a conventional photoresist wet-stripping method, a series
of operations can be performed to remove the photoresist. In some
methods, a stripping solution can be applied to the photomask,
followed by a cleaning solution, followed by a rinsing solution,
followed by drying of the photomask. One very long run or several
shorter runs are generally required to completely remove the
photoresist. A "run" refers to a stripping operation, followed by a
cleaning operation, followed by a rinsing operation, followed by a
drying operation. The stripping solution can be a wet or dry
process. In applications in which a wet strip is used, a sulfuric
hydrogen peroxide mixture (SPM) at 120.degree. C. or ozone in
deionized water (O3/DI) in a range from about 15 ppm to about 80
ppm can be used. SPM is a relatively fast stripper, but leaves
sulfur residue on the photomask. In applications in which a dry
strip is used, plasma ashing at about 150.degree. C. to about
250.degree. C. can be used. Plasma ashing can damage the ARC or
cause photomask warpage. The cleaning solution can be, for example,
deionized water or an ammonium peroxide mixture (APM). Examples of
APMs include, but are not limited to, Standard Clean-1 (SC-1) and
AM-clean.TM. (available from Applied Materials, Inc., Santa Clara,
Calif.). The rinsing solution can typically be, for example,
deionized water. Drying can be performed by spin drying and like
techniques.
EXAMPLE 1
[0006] In one experimental method, a series of runs was required to
remove a 300 nanometer (nm) thick positive e-beam photoresist from
a photomask. In run 1, O3/DI at 20 ppm was applied to a photomask
for approximately 10 minutes, followed by cleaning with deionized
water, rinsing with deionized water and spin-drying. Runs 2-4 were
a repeat of run 1. The photoresist etch rate was measured at 7.5
nm/minute by visual inspection. Total run time for the O3/DI
stripping operation was 40 minutes. Table 1 graphically illustrates
the stripping method according to the above-described method.
TABLE-US-00001 TABLE 1 Run 1 O3/DI strip - 10 minutes DI clean DI
rinse Dry Run 2 O3/DI strip - 10 minutes DI clean DI rinse Dry Run
3 O3/DI strip - 10 minutes DI clean DI rinse Dry Run 4 O3/DI strip
- 10 minutes DI clean DI rinse Dry
EXAMPLE 2
[0007] In another experimental method, at least two runs were
required to remove a 300 nm thick positive e-beam photoresist from
a photomask. In run 1, O3/DI at 20 ppm was applied to a photomask
for approximately 10 minutes, followed by cleaning with AM-clean,
rinsing with deionized water and spin-drying. For the final
cleaning operation, DI water can be used with megasonic power at a
frequency from about 5 revolutions per minute (rpm) (0.52 radians
per second (rad/s)) to about 15 rpm (1.57 rad/s). Run 2 was a
repeat of run 1. The photoresist etch rate was measured at 15
nm/min by visual inspection, Total run time for the O3/DI stripping
operation was 20 minutes. Table 2 graphically illustrates the
stripping method according to the above-described method.
TABLE-US-00002 TABLE 2 Run 1 O3/DI strip - 10 minutes AM-clean DI
rinse Dry Run 2 O3/DI strip - 10 minutes AM-clean DI rinse Dry
SUMMARY OF INVENTION
[0008] Embodiments of methods for decreasing the process time for
photoresist stripping from photomasks are herein disclosed. In some
embodiments, a stripping solution and a cleaning solution are
consecutively applied in an alternating manner to a photomask to
remove photoresist from the mask. The stripping solution and the
cleaning solution can each be applied between 6 and 12 times. The
stripping solution and the cleaning solution can be applied in a
predetermined time interval from about 30 seconds to about 120
seconds and from about 8 seconds to about 30 seconds, respectively.
The process can include a finishing process which can include a
final cleaning operation, a rinsing operation and a drying
operation.
BRIEF DESCRIPTION OF DRAWINGS
[0009] FIGS. 1A-1E illustrate a process of fabricating a
photomask.
[0010] FIG. 2 is a schematic illustration of a method of stripping
a photoimageable material according to an embodiment of the present
invention.
[0011] FIG. 2A illustrates an apparatus which can be used to strip
a photoimageable material from a photomask according to embodiments
of the present invention.
[0012] FIG. 2B illustrates a nozzle of the apparatus of FIG.
2A.
[0013] FIG. 3 illustrates a contactor device which may be used
according to embodiments of the present invention.
DETAILED DESCRIPTION
[0014] Methods for removing photoresist from a photomask during a
photomask fabrication process can be performed in accordance with
embodiments of the present invention. In one embodiment, a
stripping operation and a cleaning operation can be performed on a
photomask in a consecutively alternating manner until the
photoresist is substantially or completely removed. In some
embodiments, a final cleaning operation, a rinsing operation and a
drying operation can be performed thereafter.
[0015] FIGS. 1A-1E illustrate a typical process flow for forming a
photomask. In FIG. 1A, a substrate 105 is coated with a
chrome-containing layer 110 followed by a coating of a photoresist
(PR) layer 115 to form photomask template 100. A photomask template
can include a quartz, a glass or a sapphire substrate, a
metal-containing layer (such as a chrome-containing,
molybdenum-containing, or tungsten-containing material, for
example), an ARC layer and a photoresist layer. In one embodiment,
the photoresist layer is combined with an anti-reflective coating
material. The metal-containing layer can be from about 300 nm to
about one micrometer (.mu.m), while the photoresist layer can be
from about 3000 Angstroms (A) to about 50,000 .ANG.. Photomask
sizes range from about 3 in.sup.2 (7.62 cm.sup.2) to 11 in.sup.2
(27.94 cm.sup.2), preferably 5 in.sup.2 (12.7 cm.sup.2) to 6
in.sup.2 (15.24 cm.sup.2). In one embodiment, substrate 105 is a
quartz substrate between about 5 in.sup.2 (12.7 cm.sup.2) to 6
in.sup.2 (15.24 cm.sup.2). Chrome-containing layer 110 may be
formed by a process such as sputtering. Photoresist layer 115 may
be formed by a spinning process followed by polymerization and
hardening.
[0016] In FIG. 1B, photomask template 100 is subjected to e-beam or
laser lithography equipment to write (arrows 120) a predetermined
pattern 125 (not shown in this figure) on the surface of
photoresist layer 115. In FIG. 1C, developer chemicals can be
applied to photomask template 100 to finalize predetermined pattern
125 over the photoresist area which was exposed by the e-beam or
laser. The developer chemicals only remove photoresist in the areas
subjected to the e-beam or laser. In FIG. 1D, dry or wet etching
can be used to etch chrome-containing layer 110 in the areas in
which the photoresist has been removed from photomask template 100.
The area covered by the remaining photoresist remains
unaffected.
[0017] In FIG. 1E, remaining photoresist is removed via a strip
process (wet or dry), followed by cleaning and drying operations.
At this stage, the surface of photomask template 100 is composed of
dark areas covered by chrome-containing material or clear areas in
which the chrome-containing material has been removed (naked
quartz). The quartz is able to transmit incoming light from a light
source. The patterned photomask template is typically referred to
as a photomask.
[0018] In some embodiments, photoresist layer 115 shown in FIG. 1D
can be removed according to the process set forth in FIG. 2.
Specifically, a stripping solution and a cleaning solution can be
consecutively applied in an alternating manner for a predetermined
time interval prior to a final cleaning operation, a rinse
operation and a drying operation to remove photoresist from a
photomask. The photoresist (or photoimageable material) can be a
positive or a negative photoresist. Examples of positive
photoresists include, but are not limited to, FEP and iP3600, while
an example of a negative photoresist includes, but is not limited
to, NEB.
[0019] As set forth in block 290, a photoresist stripping solution
can be applied to a photomask. The stripping solution can be an SPM
or O3/DI. In some embodiments, the stripping solution can be O3/DI
in a range from about 15 ppm to about 35 ppm of ozone. In one
embodiment, the stripping solution is O3/DI at 20 ppm. The
stripping solution can be applied for a time interval from between
about 30 seconds to about 60 120 seconds. In one embodiment, the
stripping solution is applied for about 60 seconds. The stripping
solution can be applied to the photomask while the photomask is
spinning in a process apparatus such as the Applied Materials
Tempest (available from Applied Materials, Santa Clara, United
States). In some embodiments, the rotation during application of
the stripping solution is between about 50 rpm (5.23 rad/s) and 300
rpm (31.42 rad/s). In an alternative embodiment, a dry strip, such
as plasma ashing, can be performed in lieu of the wet strip.
[0020] Next, as set forth in block 292, a cleaning solution can be
applied to the photomask. The cleaning solution can be an APM
including, but not limited to, SC-1 or AM-clean. AM-clean is a
solution resulting from the mixture of ammonium hydroxide
(NH.sub.4OH), hydrogen peroxide (H.sub.2O.sub.2), water (H.sub.2O),
a chelating agent and a surfactant. The mixture of ammonium
hydroxide, surfactant and chelating agent is sold in a proprietary
blend known as AM1 (available from Mitsubishi Chemical Corporation,
Tokyo, Japan). As known by those skilled in the art, these
compounds only dissociate into their respective ions and no
chemical reactions occur among these compounds in a combined
solution. The ammonium hydroxide, hydrogen peroxide and water can
be present in concentrations defined by dilution ratios of between
5:1:1 to 1000:1:1, respectively. The ammonium hydroxide/hydrogen
peroxide ratio can also be varied between 0.05:1 and 5:1. In some
embodiments, no hydrogen peroxide is used at all. The ammonium
hydroxide can be from a solution of about 28-29% by weight (w/w) of
NH.sub.3 to water. The hydrogen peroxide can be from a solution of
about 31-32% w/w of H.sub.2O.sub.2 to water. The ammonium hydroxide
and the hydrogen peroxide can remove particles and residual organic
contaminates from a photomask after application of the stripping
solution. According to some embodiments, the cleaning solution has
an alkaline pH level between about 9 and 12, more specifically,
between about 10 and 11.
[0021] The chelating agent can remove metallic ions from the
photomask. Chelating agents are also known as complexing or
sequestering agents. These agents have negatively charged ions
called ligands that bind with free metal ions and form a combined
complex that will remain soluble. The ligands bind to the free
metal ions as follows:
M.sup.x++L.sup.y-.fwdarw.M.sup.(x-y)+L
Common metallic ions that may be present include, but are not
limited to copper, iron, nickel, aluminum, calcium, magnesium and
zinc.
[0022] The surfactant can prevent reattachment or redeposition of
particles on the photomask after they have been dislodged from the
photomask. Preventing the reattachment of the particles is
important because allowing the particles to reattach increases
overall cleaning time. Surfactants are long hydrocarbon chains that
typically contain a hydrophilic (polar water-soluble group) and a
hydrophobic group (non-polar water-insoluble group). The surfactant
may be non-ionic, anionic or a mixture of non-ionic and anionic
compounds. Non-ionic means that the polar end of the surfactant has
an electrostatic rather than an ionic charge and anionic means that
the polar end of the surfactant has a negative ionic charge.
[0023] In one embodiment, the cleaning solution is
AM1/H.sub.2O.sub.2/DI at a ratio of 1:2:80, respectively. The
amount of ammonium hydroxide in the AM1 solution can be between
about 28% to 29% w/w of NH.sub.3/water and the hydrogen peroxide
can be from about 31% to 32% w/w of H.sub.2O.sub.2/water, The
cleaning solution can be applied in a time interval from between
about 10 seconds to about 15 seconds. In one embodiment in which
the photoresist is either positive or negative and the cleaning
solution is AM-clean, the cleaning solution can be applied for
about 10 seconds. The cleaning solution can be applied to the
photomask while the photomask is spinning in a process apparatus.
In some embodiments, the rotation during application of the
cleaning solution is between about 50 rpm (5.23 rad/s) and 300 rpm
(31.42 rad/s).
[0024] As shown by arrows 288 in FIG. 2, the stripping solution and
the cleaning solution can be applied repeatedly until the
photoresist is substantially or completely removed from the
photomask. In some embodiments, the stripping solution and the
cleaning solution can be applied in a consecutive alternating
manner between 6 and 12 times each. In one embodiment in which the
photoresist is either negative or positive and the cleaning
solution is AM-clean, the stripping solution and the cleaning
solution is each applied 9 times each to the photomask in a
consecutive alternating manner. In some embodiments, the stripping
solution can change throughout the process. For example, in one
embodiment, a stripping solution of O3/DI can be applied to the
photomask, followed by a cleaning solution, followed by a stripping
solution of SPM, followed by a cleaning solution and thereafter
repeated using different combinations of stripping solution until
the photoresist is substantially or completed removed from the
photomask. Similarly, in another embodiment, a stripping solution
can be applied to the photomask, followed by a cleaning solution of
AM-clean, followed by a stripping solution, followed by a cleaning
solution of DI water and thereafter repeated using different
combinations of cleaning solution until the photoresist is
substantially or completed removed from the photomask. Any
combination of stripping and cleaning solutions is contemplated by
embodiments of the present invention. In some embodiments, a final
cleaning operation, a rinsing operation and a drying operation may
be performed after the photoresist is substantially or completely
removed from the photomask by repeating a stripping operation and a
cleaning operation in an alternating consecutive manner according
to the embodiments previously described.
[0025] Following a series of consecutive alternating applications
of a stripping solution and a cleaning solution, the photomask can
be subjected to a final cleaning operation as set forth in block
294. The final cleaning operation can be performed with, for
example, deionized water or an APM cleaning solution including SC-1
or AM-clean. In addition, using AM-clean, the final cleaning
operation can be performed using megasonic power at between about
900 kilohertz (kHz) to about 1000 kHz and a frequency from about 5
rpm (0.52 rad/s) to about 30 rpm (3.14 rad/s) for between about 60
seconds and 120 seconds.
[0026] Following the final cleaning operation, the photomask can be
rinsed as set forth in block 296. The rinsing operation can be
performed with, for example, deionized water at a frequency from
about 150 rpm (15.71 rad/s) to about 200 rpm (20.94 rad/s) for
between about 60 seconds and 120 seconds. In one embodiment, the
frequency for the rinsing operation is about 200 rpm (20.94 rad/s).
Generally, no megasonic power is used in the rinsing operation.
[0027] Following the rinsing operation, the photomask can be
subjected to a drying operation as set fort in block 298. The
drying operation can be, for example, spin drying or like
techniques. In spin drying, the photomask can rotate between about
700 rpm (73.30 rad/s) and about 1000 rpm (104.72 rad/s) for between
about 40 seconds and 60 seconds. According to embodiments of the
present invention, the time required for the photoresist stripping
operation in photomask process can be reduced from between two to
four times compared to conventional methods.
[0028] In an experimental method according to an embodiment of the
present invention, one run was required to remove a 300 nm thick
FEP positive e-beam photoresist from a photomask following an
etching process. The run included consecutively alternating
applications of O3/DI stripping solution at 20 ppm and AM-clean
(abbreviated "AM" in Table 3 below) at a ratio of 1:2:80
AM1/H.sub.2O.sub.2/DI, respectively. The stripping solution was
applied for about 60 seconds, while the cleaning solution was
applied for about 10 seconds. The consecutive alternating
operations were repeated nine times for a total run time of 10.5
minutes, including time to switch the stripping solution to the
cleaning solution. The total time for the cumulative stripping
solution applications was 9 minutes. Following application of the
O3/DI solution and AM-clean solution in alternating operations, a
final AM-clean solution was applied to the photomask, followed by a
deionized water rinse, followed by spin-drying. The photoresist
etch rate was measured at 33.3 nm/min by visual inspection by
measuring the process time to remove the photoresist from the top
surface of the photomask. Table 3 graphically illustrates the
stripping method according to the above-described method.
TABLE-US-00003 TABLE 3 Run 1 O3/DI AM O3/DI AM O3/DI AM O3/DI AM
O3/DI AM O3/DI Run 1 AM O3/DI AM O3/DI AM O3/DI AM AM-clean DI
Rinse Dry
TABLE-US-00004 TABLE 4 No. of runs Total O3/DI PR to strip time
etch rate Test Process PR (min.) (nm/min.) 1 10 min O3/DI; DI
clean; 4 40 7.5 DI rinse; dry 2 10 min O3/DI; AM 2 20 15 clean; DI
rinse; dry 3 9x (1 min. O3/DI/10 sec. 1 9 33.3 AM clean); AM clean;
DI rinse, dry
As can be observed in Table 4, test 3 performed in accordance with
embodiments of the present invention resulted in an accelerated
photoresist stripping process for both positive and negative
photoresist relative to conventional methods. For both positive and
negative photoresists, it is theorized that, in accordance with
embodiments of the present invention, the abbreviated O3/DI
operation oxidizes and dissociates the surface of the photoresist
and the abbreviated APM operation removes the modified surface
layer resulting in significantly enhanced removal rates.
[0029] Embodiments of the present invention can be performed using
a single substrate apparatus such as that illustrated in FIG. 2A.
Single substrate stripping and/or cleaning apparatus 200 shown in
FIG. 2A includes a plate 205 with a plurality of acoustic or sonic
transducers 210 located thereon. Plate 205 is preferably made of
aluminum but can be formed of other materials such as, but not
limited to, stainless steel and sapphire. Plate 205 is preferably
coated with a corrosion resistant fluoropolymer such as Halar. In
some embodiments, transducers 210 are attached to the bottom
surface of plate 205 by an epoxy. Transducers 210 can substantially
cover the entire bottom surface of plate 205, preferably at least
80% of plate 205. In one embodiments, there are four transducers
210 covering the bottom surface of plate 205 in a quadrant
formation and preferably covering at least 80% of plate 205. The
transducers 210 preferably generate megasonic waves in the
frequency range above 350 kHz. The specific frequency is dependent
on the thickness of the substrate and is chosen by its ability to
effectively provide megasonics to both sides of the substrate. In
some embodiments, the transducers are piezoelectric devices. The
transducers 210 create acoustic or sonic waves in a direction
perpendicular to the surface of a substrate 215. Substrate 215 can
be, for example, a photomask.
[0030] Substrate 215 is horizontally held by a substrate support
220 and is positioned parallel to and spaced-apart from the top
surface of plate 205. Substrate 215 can be clamped face-up by
substrate support 220 by a plurality of clamps 225. Alternatively,
the substrate can be supported on elastomeric pads on posts and
held in place by gravity. Substrate 215 faces patterned side up
towards a nozzle 230 for spraying chemicals thereon and the
opposite side of substrate 215 faces plate 205.
[0031] In one embodiment, substrate 215 is held about 3 mm above
the surface of plate 205 during a photoresist stripping process. In
some embodiments, photoresist stripping process includes
consecutively alternating applications of O3/DI stripping solution
and AM-clean cleaning solution to substrate 215 prior to a final
cleaning operation (see FIG. 2, 294) and a rinsing operation (see
FIG. 2, 296) using nozzle 230. A drying operation can follow
thereafter (see FIG. 2, 298). Stripping solution can be applied in
a predetermined time interval, such as, for example, 30 seconds to
about 120 seconds. Cleaning solution can also be applied in a
predetermined time interval, such as, for example, from about 8
seconds to about 120 seconds. In some embodiments, stripping
solution can be 20 ppm and AM-clean can be at a ratio of 1:2:80
AM1/H.sub.2O.sub.2/DI, respectively. In some embodiments, substrate
support 220 can horizontally rotate or spin substrate 215 about its
central axis at a rate of between 0-6000 rpms. Spinning can be used
in the photoresist stripping application, photoresist cleaning
application as well as the final cleaning process, final rinse
process and drying. Apparatus 200 can include a sealable chamber
235 in which nozzle 230, substrate 215, and plate 205 are located
as shown in FIG. 2A.
[0032] In an embodiment of the present invention, deionized water
is fed through a feed-through channel 240 of plate 205 and fills
the gap between the backside of substrate 215 and plate 205 to
provide a water-filled gap 245 through which acoustic waves
generated by transducers 210 can travel to substrate 215. In some
embodiments, the feed channel 240 is slightly offset from the
center of the substrate by approximately 1 mm. The backside of the
substrate may alternately be rinsed with other solutions during
this operation. In an embodiment of the present invention, DI water
fed between substrate 215 and plate 205 is degassed so that
cavitation is reduced in the DI water-filled gap 245 where the
acoustic waves are strongest thereby reducing potential damage to
substrate 215. DI water can be degassed by well known techniques at
either the point of use or back at the source.
[0033] Stripping solutions and rinsing water such as DI water can
be expelled through nozzle 230 to generate a spray 250 on substrate
215. In some embodiments, nozzle 230 can move in a horizontal plane
to uniformly apply chemical solutions to substrate 215. In some
embodiments, tank 255 containing a solution for cleaning (an APM or
deionized water) is coupled to conduit 260 which feeds into nozzle
230. In an embodiment of the present invention, the diameter of
conduit 260 has a reduced cross-sectional area or a "venturi" 265
that is shown in more detail in FIG. 2B, in a line before spray
nozzle 230 at which point a gas (such as ozone) from tank 270a that
travels through conduit 275a, is dissolved in deionized water from
tank 270b traveling through conduit 275b as it travels to nozzle
230. "Venturi" 265 enables a gas to be dissolved into a fluid flow
280 (see FIG. 2B) at gas pressure less than the pressure of the
liquid flowing through conduit 260. The venturi 265 creates
dissolution under pressure locally because of the increase in flow
rate at the venturi. In an alternate embodiment, gases are
dissolved into the solution by a hydrophobic contactor device 300
as shown in FIG. 3. This contactor device 300 is put into the
conduit 260. Contactor device 300 has a hydrophobic membrane
conduit 300 which allows gasses to pass through but not water. Gas
310 is fed into membrane conduit 305 where the gas dissolves into
the liquid passing through the area 315.
[0034] Prior to being fed through nozzle 230, deionized water can
be ozonated at point of use by dissolving O.sub.3 gas into the
deionized water forming a photoresist stripping solution (see FIG.
2, 290) for application to substrate 215 thereof. This may be done
with a venturi device as described with respect to FIG. 2B or with
a membrane device as described with respect to FIG. 3. Dissolved
ozone (O.sub.3) is added to the deionized water in a concentration
of about 20 ppm or greater to serve as an oxidant. The solution
should have an oxidation potential sufficient to oxidize the most
noble metal in the solution. Copper (Cu.sup.2+), with a standard
reduction potential of 0.3V, is usually the most noble metal
present. Therefore a standard reduction potential of greater than
0.5V is desired. Ozone will solvate the metal ions and prevents
precipitation by oxidizing the metal ions that are in solution.
This will help decrease the processing time by making the rinsing
more effective. The use of ozone is also efficient and cost
effective. In an embodiment of the present invention, the DI rinse
water is degassed prior to dissolving ozone into the deionized
water.
[0035] Although discussed with respect to a photomask, embodiments
of the present invention can be applied to other substrates, such
as, but not limited, semiconductor wafers. One of ordinary skill in
the art will appreciate that the embodiments of the present
invention can be performed on a variety of different
substrates.
[0036] In the foregoing specification, specific embodiments have
been described. It will, however, be evident that various
modifications and changes can be made thereto without departing
from the broader spirit and scope of the appended claims. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense.
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